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Thermodynamics of Pure-Silica Molecular Sieve Synthesis

Piccione, Patrick M. and Yang, Sanyuan and Navrotsky, Alexandra and Davis, Mark E. (2002) Thermodynamics of Pure-Silica Molecular Sieve Synthesis. Journal of Physical Chemistry B, 106 (14). pp. 3629-3638. ISSN 1520-6106. doi:10.1021/jp014427j.

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The thermodynamics of pure-silica molecular sieves (denoted by their structural codes ^*BEA, MFI, MTW, and STF) are investigated by solution calorimetry at 323.15 K using 25% aqueous HF as solvent. The enthalpies of solution are determined for both calcined (silica frameworks) and organic structure-directing agent (SDA) occluded samples (SDAs:  tetraethylammonium (TEA), tetrapropylammonium (TPA), trimethylenebis(N-methyl,N-benzylpiperidinium) (BISPIP), and 2,6-dimethyl-1-aza-spiro[5.4]decane (SPIRO)). These measurements provide data that enable the determination of the following interaction enthalpies between the molecular sieve frameworks and SDAs at 323.15 K: ^*BEA/TEA, −3.1 ± 1.4 kJ/mol SiO_2 (−32 ± 15 kJ/mol SDA); ^*BEA/BISPIP, −5.9 ± 0.7 kJ/mol SiO_2 (−181 ± 21 kJ/mol SDA); MFI/TEA, −1.1 ± 1.4 kJ/mol SiO_2 (−27 ± 33 kJ/mol SDA); MFI/TPA, −3.2 ± 1.4 kJ/mol SiO_2 (−81 ± 34 kJ/mol SDA); MTW/BISPIP, −1.6 ± 1.3 kJ/mol SiO_2 (−124 ± 97 kJ/mol SDA); and STF/SPIRO, −4.9 ± 0.9 kJ/mol SiO_2 (−83 ± 16 kJ/mol SDA). Interaction entropies are estimated, and when used in combination with the measured interaction enthalpies, provide the following Gibbs free energies of interaction between the SDAs and the molecular sieve frameworks: ^*BEA/TEA, −5.4 ± 1.5 kJ/mol SiO_2; MFI/TEA, −2.0 ± 1.4 kJ/mol SiO_2; and MFI/TPA, −4.9 ± 1.4 kJ/mol SiO2. The energetics of the synthesis of molecular sieves (considering all components present in the synthesis mixture) are examined and reveal small differences between various molecular sieve/SDA combinations. Assuming complete transformation of the starting amorphous silica into a molecular sieve, the Gibbs free energy changes for the crystallization are ^*BEA/TEA, −8.5 ± 2.9 kJ/mol SiO_2; MFI/TEA, −4.9 ± 2.8 kJ/mol SiO_2; and MFI/TPA, −8.1 ± 2.8 kJ/mol SiO_2. No single factor (enthalpy, entropy, etc.) dominates the overall Gibbs free energies, and these small energetic differences suggest that kinetic factors are of major importance in molecular sieve preparation.

Item Type:Article
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Navrotsky, Alexandra0000-0002-3260-0364
Davis, Mark E.0000-0001-8294-1477
Additional Information:© 2002 American Chemical Society. Received 5 December 2001. Published online 19 March 2002. Published in print 1 April 2002. Financial support for this work was provided by the Chevron Research and Technology Co. The calorimetric studies were supported by NSF grants DMR 9731782 and 0101391. P.M.P. thanks Dr. Stacey Zones (Chevron) for providing the STF and 2,6-dimethyl-1-aza-spiro[5.4]decane samples used in this study, and Michael Gordon and Michael Roy (Caltech) for helping in the calorimeter cell design. Additionally, we thank Dr. Stacey Zones (Chevron) for many helpful discussions.
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Chevron Research and Technology Co.UNSPECIFIED
Issue or Number:14
Record Number:CaltechAUTHORS:20170518-083547580
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Official Citation:Thermodynamics of Pure-Silica Molecular Sieve Synthesis Patrick M. Piccione, Sanyuan Yang, Alexandra Navrotsky, and Mark E. Davis The Journal of Physical Chemistry B 2002 106 (14), 3629-3638 DOI: 10.1021/jp014427j
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77552
Deposited By: Ruth Sustaita
Deposited On:18 May 2017 18:38
Last Modified:15 Nov 2021 17:32

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